(CNN) -- A Malaysia Airlines passenger jet crashed in a rebel-controlled part of eastern Ukraine on Thursday, spurring swift accusations from Ukrainian officials that "terrorists" shot down the aircraft.

The United States has concluded a missile shot down the plane, but hasn't pinpointed who was responsible, a senior U.S. official told CNN's Barbara Starr.

The Boeing 777 with 298 people aboard fell from the sky near the town of Torez in the Donetsk region of eastern Ukraine, officials said. A top Ukrainian official said the plane, which was on the way from Amsterdam to Kuala Lumpur, was flying at about 10,000 meters (nearly 33,000 feet) when the missile hit.

A radar system saw a surface-to-air missile system turn on and track an aircraft right before the plane went down, the senior U.S. official said. A second system saw a heat signature at the time the airliner was hit, the official said. The United States is analyzing the trajectory of the missile to try to learn where the attack came from, the official said.

The Obama administration believes Ukraine did not have the capability in the region -- let alone the motivation -- to shoot down the plane, a U.S. official told CNN's Jake Tapper.

What we know about the MH17 crash

Flight attendant loses friends on MH17

Malaysian Prime Minister Najib Razak said the plane never made a distress call.

He called for an international team to have full access to the crash site.

Debris from Malaysia Airlines Flight 17 sits in a field at the crash site in Hrabove, Ukraine, on Tuesday, September 9. The Boeing 777 is believed to have been shot down July 17 in an area of eastern Ukraine controlled by pro-Russian rebels.

Australian and Dutch experts examine the area of the crash on Sunday, August 3.

A woman walks with her bicycle near the crash site on Saturday, August 2.

Police secure a refrigerated train loaded with bodies of passengers from Malaysia Airlines Flight 17 as it arrives in a Kharkiv, Ukraine, factory on Tuesday, July 22.

A pro-Russian rebel passes wreckage from the crashed jet near Hrabove on Monday, July 21.

Wreckage from the jet lies in grass near Hrabove on July 21.

A man covers his face with a rag as members of the Organization for Security and Co-operation in Europe and the Dutch National Forensic Investigations Team inspect bodies in a refrigerated train near the crash site in eastern Ukraine on July 21.

Emergency workers carry a victim's body in a bag at the crash site on July 21.

A piece of the plane lies in the grass in eastern Ukraine's Donetsk region on July 21.

An armed pro-Russian rebel stands guard next to a refrigerated train loaded with bodies in Torez, Ukraine, on Sunday, July 20.

Ukrainian State Emergency Service employees sort through debris on July 20 as they work to locate the deceased.

A woman covers her mouth with a piece of fabric July 20 to ward off smells from railway cars that reportedly contained passengers' bodies.

Toys and flowers sit on the charred fuselage of the jet as a memorial on July 20.

People search a wheat field for remains in the area of the crash site on July 20.

A woman walks among charred debris at the crash site on July 20.

Emergency workers load the body of a victim onto a truck at the crash site on Saturday, July 19.

Emergency workers carry the body of a victim at the crash site on July 19.

A large piece of the main cabin is under guard at the crash site on July 19.

Victims' bodies are placed by the side of the road on July 19 as recovery efforts continue at the crash site. International officials lament the lack of a secured perimeter.

A man looks through the debris at the crash site on July 19.

An envelope bearing the Malaysia Airlines logo is seen at the crash site on July 19.

Armed rebels walk past large pieces of the Boeing 777 on July 19.

Ukrainian rescue workers walk through a wheat field with a stretcher as they collect the bodies of victims on July 19.

A woman looks at wreckage on July 19.

Pro-Russian rebels stand guard as the Organization for Security and Co-operation in Europe delegation arrives at the crash site on Friday, July 18.

A woman walks through the debris field on July 18.

Pro-Russian rebels stand guard at the crash site.

Wreckage from Flight 17 lies in a field in Shaktarsk, Ukraine, on July 18.

A man covers a body with a plastic sheet near the crash site on July 18. The passengers and crew hailed from all over the world, including Australia, Indonesia, Malaysia, Germany and Canada.

A diver searches for the jet's flight data recorders on July 18.

Coal miners search the crash site.

Wreckage from the Boeing 777 lies on the ground July 18.

People search for bodies of passengers on July 18.

A woman walks past a body covered with a plastic sheet near the crash site July 18.

Belongings of passengers lie in the grass on July 18.

People inspect the crash site on Thursday, July 17.

People walk amid the debris at the site of the crash.

Debris smoulders in a field near the Russian border.

Fire engines arrive at the crash site.

A man stands next to wreckage.

Debris from the crashed jet lies in a field in Ukraine.

Family members of those aboard Flight 17 leave Schiphol Airport near Amsterdam, Netherlands.

A large piece of the plane lies on the ground.

Luggage from the flight sits in a field at the crash site.

A couple walks to the location at Schiphol Airport where more information would be given regarding the flight.

Flight arrivals are listed at the Kuala Lumpur International Airport in Sepang, Malaysia.

Debris from the Boeing 777, pictured on July 17.

A man inspects debris from the plane.

Wreckage from the plane is seen on July 17.

A man talks with security at Schiphol Airport on July 17.

Wreckage burns in Ukraine.

A man stands next to the wreckage of the airliner.

People inspect a piece of wreckage believed to be from Malaysia Airlines Flight 17. This image was posted to Twitter.

People inspect a piece of wreckage believed to be from Malaysia Airlines Flight 17. This image was posted to Twitter.

A piece of wreckage believed to be from Malaysia Airlines Flight 17. This image was posted to Twitter.

A piece of wreckage believed to be from MH17. This image was posted to Twitter.

An airsickness bag believed to be from MH17. This image was posted to Twitter.

A piece of wreckage believed to be from MH17. This image was posted to Twitter.

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

Malaysia Airlines jet crashes in Ukraine

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Malaysia Airlines jet crashes in Ukraine

Deadly airline disasters

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"We must and we will find out precisely what happened to this flight. No stone will be left unturned," he said.

"If it transpires that the plane was indeed shot down, we insist that the perpetrators must swiftly be brought to justice," Najib said.

Ukrainian officials maintained that pro-Russian separatists were behind the crash.

The timeline before MH17 crashed

Russian President Vladimir Putin said Ukraine's military campaign against the separatists was to blame.

"This tragedy would not have happened, if there had been peace on that land, or in any case, if military operations in southeastern Ukraine had not been renewed," Putin said in televised remarks. "And without a doubt the government of the territory on which it happened bears responsibility for this frightening tragedy."

Ukraine's state security chief accused two Russian military intelligence officers of involvement and said they must be punished.

Valentyn Nalyvaichenko said he based his allegation on intercepts of phone conversations between the two officers. "Now you know who carried out this crime. We will do everything for the Russian military who carried out this crime to be punished," he told reporters.

The jet plunged toward the ground in a fireball, leaving a trail of black smoke behind in the sky.

Emergency crews scrambled to what witnesses described as a staggering scene of death and utter destruction.

"People said the plane kind of exploded in the air, and that everything rained down in bits and pieces, the plane itself, the people inside," said Noah Sneider, an American freelance journalist who interviewed witnesses at the scene.

Charred wreckage stretched for kilometers, he said. Stunned rescue workers and rebel fighters combed the area, Sneider said, planting sticks with white cotton ribbons where they found bodies in the fields.

"As you walk through the fields, you see a man with his cracked iPhone sticking out of his pocket. You see sort of people's clothing everywhere. Most of it's kind of ripped off by the air. There's some suitcases and stuff in a pile by the road," Sneider said.

There were many bodies left to be found as night fell, he said, and people were trying to figure out what to do next.

Locals in the rural area trying to help were overwhelmed, he said. Firemen who rushed to put out the flames found they had a hose with holes in it, spraying water everywhere, he said.

"One man said to me, 'Nothing's happened in this village for 30 years, and now this,'" Sneider said.

As details emerge, accusations fly

Details -- and accusations -- quickly poured in about Thursday's crash, which came the same week that Ukrainian officials said a Russian fighter shot down a Ukrainian military transport plane while the aircraft was in Ukrainian airspace.

Anton Gerashchenko, adviser to the Ukrainian Interior Ministry, said in a Facebook post that "terrorists" fired on the plane operating a Buk surface-to-air missile system.

Report: Malaysia plane crashes in Ukraine

First images of Malaysia Airlines debris

Ukrainian President Petro Poroshenko described the crash as a "terrorist action."

"We do not exclude that the plane was shot down and confirm that the Ukraine Armed Forces did not fire at any targets in the sky," Ukrainian President Petro Poroshenko said, according to his website.

CNN's Richard Quest, an aviation expert, said that it would be "extremely unusual" for an airliner at nearly 33,000 feet to be shot down.

From the ground, one could simply look up and tell whether a plane was a commercial aircraft, he said. "So something is absolutely appalling that's gone on here."

U.S. Vice President Joe Biden said that Ukraine's president had accepted an offer of U.S. experts to help investigate the crash.

"They will be on their way rapidly to see if we can get to the bottom of this," he said.

Biden said the plane was apparently shot down, adding "not an accident, blown out of the sky."

Who was on the plane?

The 15 crew members on Malaysia Airlines Flight 17 were all Malaysian nationals, officials said.

Malaysia Airlines also gave a breakdown of the known nationalities of the 283 passengers: 154 were Dutch, 27 were Australians, 28 were Malaysians, 12 were Indonesian, nine were from the United Kingdom, four were from Germany; four were from Belgium, three were from the Philippines and one was Canadian. Authorities were still trying to determine the nationalities of the other passengers.

The International AIDS Society said in a statement that "a number of colleagues and friends" were on the plane, on the way to attend the 20th International AIDS Conference in Melbourne, Australia.

"At this incredibly sad and sensitive time the IAS stands with our international family and sends condolences to the loved ones of those who have been lost to this tragedy," the statement said.

Russia-Ukraine dispute

The route the Malaysian plane was on, between Kuala Lumpur and the Netherlands, is a common one, CNN aviation safety consultant Mary Schiavo said Thursday. She said that the plane was flying over a troubled area and that close communication with air traffic controllers would be a key necessity.

Torez is in a rebel-held area.

In hostile or disputed areas, "any alteration from your course, and you can have a problem," Schiavo said.

Map: Approximate route of MH17

Map: Approximate route of MH17

Tensions have been high between Ukraine and Russia since street protests forced former pro-Moscow President Viktor Yanukovych from power in February. Russia subsequently annexed Ukraine's southeastern Crimea region, and a pro-Russian separatist rebellion has been raging in Ukraine's eastern Luhansk and Donetsk regions.

Ukrainian forces have been struggling to quell the separatist unrest. Ukraine's government has accused Russia of allowing weapons and military equipment, including tanks, to cross the border illegally into the hands of pro-Russian separatists.

The Pentagon said Wednesday that Russia now has 12,000 troops on the border with Ukraine, as well as some heavy weapons. The troop numbers had fallen to about 1,000 previously from a high of an estimated 40,000 forces earlier this year.

On Thursday, CNN reported that Ukrainian officials said a Russian fighter shot down a Ukrainian jet Wednesday as the jet flew in Ukrainian airspace.

Tensions are high over that incident, separate from the breaking news of the Malaysian flight Thursday.

Three months ago, the U.S. Federal Aviation Administration prohibited U.S. airlines from flying in areas not far from where Flight 17 reportedly crashed Thursday. "Due to the potential for conflicting air traffic control instructions from Ukrainian and Russian authorities and for the related potential misidentification of civil aircraft, United States flight operations are prohibited until further notice in the airspace over Crimea, the Black Sea and the Sea of Azov," the FAA said in April. Thursday's plane crash reportedly was in eastern Ukraine, scores of miles north-northeast of the Sea of Azov.

On Thursday, French transportation official Frederic Cuvillier ordered that French airlines avoid Ukrainian airspace until the cause of Thursday's Malaysia Airlines crash is known, the French Transportation Ministry said in a news release.

People inspect wreckage thought to be from Malaysia Airlines Flight 17 in Ukraine. This image was posted to Twitter.

Airline's troubles

Thursday's crash marks the second time this year that Malaysia Airlines has faced an incident involving a downed plane.

Flight 370 probably flew into the southern Indian Ocean on autopilot with an unresponsive crew, Australian authorities said last month.

During the early phase of the search for Flight 370, aircraft and ships scoured vast stretches of the surface of the southern Indian Ocean but found no debris.

Pings initially thought to be from the missing plane's flight recorders led to a concentrated underwater search that turned up nothing.

A new underwater search, farther south, will be broadly in an area where planes and vessels had already looked for debris on the surface of the water. It is expected to begin in August.

The first Boeing 777 entered service in June 1995, and the airplane has flown almost five million flights, accumulating more than 18 million flight hours, according to Boeing's web site. The plane is capable to flying up to 43,100 feet.

What next?

I am shocked by reports that an MH plane crashed. We are launching an immediate investigation.

Aviation experts cautioned against jumping to conclusions about Thursday's crash at this early stage.

But all agreed that a massive investigation should be launched, involving parties not involved in the conflict between Ukraine and Russia,

The families of people on board will demand a transparent international investigation, and so will the global community, Quest said.

In the coming days, finding and examining the plane's data recorders will be key -- but the fact that the crash occurred in such a volatile region makes what comes next anything but certain, CNN aviation analyst and pilot Miles O'Brien said.

"The big question will be, in whose hands will they fall, and will this be a really objective, international investigation?" he said.

The wreckage path, O'Brien said, will reveal a lot. If a plane breaks up in midair, which is likely what would happen in a missile strike, there would be a large swath of wreckage, he said, but if it breaks down due to mechanical failure, the debris field would be more concentrated.